[Stoves] Dhan Hurley..... TLUD enhancements.... Whyaren'tthereany comments, except from what it seems is a Venture Capital Company?

[Andrew Heggie]

On Tue, 11 Jun 2019 at 20:03, Kirk H. <gkharris316 at comcast.net> wrote:
>

>
> Your response describes how the Joule Thief works.  Could you continue further to describe how it might work with a thermocouple (or pile) to get electricity from a wood stove, perhaps for an led light or a radio.  This might be useful information for Dhan.
>

Kirk my experience with electronics is nearly 50 years old and field
effect transistors were just discovered, these are  the very low
resistance devices which enable low loss  circuits which boost or
reduce voltage (known as buck or boost circuits as Crispin mentioned).

On the thermoelectric side I would refer you to a post, in the archive at
http://lists.bioenergylists.org/mailman/private/stoves_lists.bioenergylists.org/2016-June/011717.html

by Paul Van Sluis who worked on the Phillips stove. This used a TEG at
2% conversion to electricity, the heat being fed back into the stove
so at little heat cost.

He points out that semiconductor TEGs have a limited life because they
fail  if cycled many times. I only have one semiconductor  TEG device
which runs a fan atop my wood stove and that has survived 3 heating
seasons  so far but uses a TEG derived from a mass produced cooling
chip.

Back to the basics:

The voltage developed by the Seebeck effect "the conversion
temperature difference between two dissimilar conductors into a
voltage" is proportional to the temperature difference between the hot
and cold junctions and is tiny, so in order to work in an electric
circuit with transistors the voltage has to be multiplied by stacking
a number of these junctions into a thermopile. Once you generate a
voltage above a Volt or so then the boost devices, like Joulethief can
increase the voltage to what we need.

Metal to metal junctions produce a very small voltage difference per
degree of heat  difference between hot and cold side, they are used in
flame sensors as they withstand high temperatures but normally have an
electrically powered amplifier to operate a solenoid. Honeywell
produce(d) a metal thermopile flame sensor that produced 0.75V and
would operate a gas solenoid directly.

Semiconductor thermopiles produce higher voltages but have to be kept
below 200C, with my stove top fan this is managed by the base having a
bimetallic strip which lifts one side of the hot plate away from the
stove top slightly.

That's the voltage side but to do work you need to produce current and
this is dependant on the heat flux through the thermopile, for a
usable current you need a large thermopile and a lot of heat going
from the hot side and being removed from the cold side.

Often we already preheat combustion air in a stove and this also cools
the metal sides of a combustion chamber so there need not be a  heat
loss involved by using combustion air to cool the cold side.

In his post Philip points out that  you still need to get the stove up
to temperature and he talks of a hand cranked generator and
reliability issues, he also points out Phillips moved over to a
battery powered device charged by solar PV  as being more reliable.

If it weren't for the fact I am so ham-fisted that I fail to make
gadgets very well I would have liked to try and make a combustion
chamber made entirely from metal to dissimilar metal junctions formed
into a large circumferential pile running a 500C temperature
difference.

I hope that helps answer your question in part.

Andrew